LTC2604/LTC2614/LTC2624
Quad 16-Bit Rail-to-Rail DACs
in 16-Lead SSOP
FEATURES
DESCRIPTION
n
The LTC®2604/LTC2614/LTC2624 are quad 16-,14- and
12-bit 2.5V to 5.5V rail-to-rail voltage output DACs in
16-lead narrow SSOP packages. These parts have separate
reference inputs for each DAC. They have built-in high performance output buffers and are guaranteed monotonic.
Smallest Pin Compatible Quad 16-Bit DAC:
LTC2604: 16-Bits
LTC2614: 14-Bits
LTC2624: 12-Bits
Guaranteed 16-Bit Monotonic Over Temperature
Separate Reference Inputs for each DAC
Wide 2.5V to 5.5V Supply Range
Low Power Operation: 250μA per DAC at 3V
Individual DAC Power-Down to 1μA, Max
Ultralow Crosstalk Between DACs ( 1GΩ) when the corresponding DACs are powered down.
Normal operation can be resumed by executing any command which includes a DAC update, as shown in Table 1.
The selected DAC is powered up as its voltage output is
updated. When a DAC which is in a powered-down state
is powered up and updated, normal settling is delayed. If
less than four DACs are in a powered-down state prior to
the update command, the power-up delay time is 5μs. If on
the other hand, all four DACs are powered down, then the
main bias generation circuit block has been automatically
shut down in addition to the individual DAC amplifiers and
reference inputs. In this case, the power up delay time is
12μs (for VCC = 5V) or 30μs (for VCC = 3V).
Voltage Outputs
Each of the four rail-to-rail amplifiers contained in these
parts has guaranteed load regulation when sourcing or
sinking up to 15mA at 5V (7.5mA at 3V).
Load regulation is a measure of the amplifier’s ability to
maintain the rated voltage accuracy over a wide range of
load conditions. The measured change in output voltage
per milliampere of forced load current change is expressed
in LSB/mA.
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12
X
X
SDI
SDO
SCK
CS/LD
1
X
X
2
3
X
4
X
X
C3
SDI
X
5
X
DON’T CARE
X
C2
2
C1
3
X
X
6
X
X
7
COMMAND WORD
1
SCK
CS/LD
C0
X
X
4
8
A3
A2
6
A1
7
A0
8
D15
9
D14
10
D12
12
D11
13
D10
14
24-BIT INPUT WORD
D13
11
D9
15
D7
17
DATA WORD
D8
16
D6
18
D5
19
C1
11
C2
C1
COMMAND WORD
C2
10
C0
C0
A3
A3
A2
14
A1
15
A2
A1
ADDRESS WORD
13
A0
A0
16
17
D15
D15
PREVIOUS 32-BIT INPUT WORD
12
D14
D14
18
t2
t8
D9
D9
t4
23
PREVIOUS D15
t3
17
D10
D10
22
SDO
t1
D11
D11
21
D15
D12
D12
20
SDI
SCK
D13
D13
19
Figure 2b. LTC2604 32-Bit Load Sequence
LTC2614 SDI/SDO Data Word: 14-Bit Input Code + 2 Don’t Care Bits
LTC2624 SDI/SDO Data Word: 12-Bit Input Code + 4 Don’t Care Bits
C3
C3
9
Figure 2a. LTC2604 24-Bit Load Sequence (Minimum Input Word)
LTC2614 SDI Data Word: 14-Bit Input Code + 2 Don’t Care Bits
LTC2624 SDI Data Word: 12-Bit Input Code + 4 Don’t Care Bits
ADDRESS WORD
5
24
25
D7
D3
21
18
D7
D6
D6
26
22
D2
PREVIOUS D14
D14
D8
DATA WORD
D8
D4
20
27
D5
D5
D1
23
28
D4
D4
D0
24
D3
D3
29
2604 F02a
D2
D2
30
D1
D1
31
2604 F02b
CURRENT
32-BIT
INPUT WORD
D0
D0
32
LTC2604/LTC2614/LTC2624
OPERATION
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13
LTC2604/LTC2614/LTC2624
OPERATION
DC output impedance is equivalent to load regulation, and
may be derived from it by simply calculating a change in
units from LSB/mA to Ohms. The amplifiers’ DC output
impedance is 0.025Ω when driving a load well away from
the rails.
the device’s ground pin as possible. Ideally, the analog
ground plane should be located on the component side of
the board, and should be allowed to run under the part to
shield it from noise. Analog ground should be a continuous
and uninterrupted plane, except for necessary lead pads
and vias, with signal traces on another layer.
When drawing a load current from either rail, the output
voltage headroom with respect to that rail is limited by
the 30Ω typical channel resistance of the output devices;
e.g., when sinking 1mA, the minimum output voltage =
30Ω • 1mA = 30mV. See the graph Headroom at Rails vs
Output Current in the Typical Performance Characteristics
section.
The GND pin functions as a return path for power supply currents in the device and should be connected to
analog ground. Resistance from the GND pin to system
star ground should be as low as possible. When a zero
scale DAC output voltage of zero is desired, the REFLO pin
(pin 2) should be connected to system star ground.
The amplifiers are stable driving capacitive loads of up
to 1000pF.
Rail-to-Rail Output Considerations
In any rail-to-rail voltage output device, the output is limited
to voltages within the supply range.
Board Layout
The excellent load regulation and DC crosstalk performance
of these devices is achieved in part by keeping “signal”
and “power” grounds separate.
Since the analog outputs of the device cannot go below
ground, they may limit for the lowest codes as shown in
Figure 3b. Similarly, limiting can occur near full scale when
the REF pins are tied to VCC. If REF x = VCC and the DAC
full-scale error (FSE) is positive, the output for the highest
codes limits at VCC as shown in Figure 3c. No full-scale
limiting can occur if REF x is less than VCC – FSE.
The PC board should have separate areas for the analog
and digital sections of the circuit. This keeps digital signals
away from sensitive analog signals and facilitates the use
of separate digital and analog ground planes which have
minimal capacitive and resistive interaction with each
other.
Offset and linearity are defined and tested over the region
of the DAC transfer function where no output limiting
can occur.
Digital and analog ground planes should be joined at only
one point, establishing a system star ground as close to
VREF = VCC
VREF = VCC
POSITIVE
FSE
OUTPUT
VOLTAGE
OUTPUT
VOLTAGE
INPUT CODE
OUTPUT
VOLTAGE
(c)
0
NEGATIVE
OFFSET
0V
INPUT CODE
32,768
INPUT CODE
65,535
(a)
2600 F03
(b)
Figure 3. Effects of Rail-to-Rail Operation On a DAC Transfer Curve. (a) Overall Transfer Function (b) Effect
of Negative Offset for Codes Near Zero Scale (c) Effect of Positive Full-Scale Error for Codes Near Full Scale
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14
LTC2604/LTC2614/LTC2624
PACKAGE DESCRIPTION
GN Package
16-Lead Plastic SSOP (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1641)
.189 – .196*
(4.801 – 4.978)
.045 ±.005
16 15 14 13 12 11 10 9
.254 MIN
.009
(0.229)
REF
.150 – .165
.229 – .244
(5.817 – 6.198)
.0165 ± .0015
.150 – .157**
(3.810 – 3.988)
.0250 BSC
RECOMMENDED SOLDER PAD LAYOUT
1
.015 ± .004
× 45°
(0.38 ± 0.10)
.007 – .0098
(0.178 – 0.249)
2 3
4
5 6
7
.0532 – .0688
(1.35 – 1.75)
8
.004 – .0098
(0.102 – 0.249)
0° – 8° TYP
.016 – .050
(0.406 – 1.270)
NOTE:
1. CONTROLLING DIMENSION: INCHES
INCHES
2. DIMENSIONS ARE IN
(MILLIMETERS)
.008 – .012
(0.203 – 0.305)
TYP
.0250
(0.635)
BSC
GN16 (SSOP) 0204
3. DRAWING NOT TO SCALE
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
2604fd
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
LTC2604/LTC2614/LTC2624
TYPICAL APPLICATION
5V
5V
1k
1k
10k
10k
0.1μF
10k
0.01μF
0.1μF
10k
20Ω
49.9Ω
70MHz IN
47pF
ZC830
0.01μF
OUT
10pF
49.9Ω
20pF
49.9Ω
ZC830
DAC A
DAC B
DAC C
DAC D
OPTIONAL
20k
0.1μF
OPTIONAL
20k
0.1μF
CS/LD
SCK
SDI
LTC2604
5V
5V
LO
2.74k
1%
100k
2.74k
1%
100k
2.74k
1%
90°
2.74k
1%
I+Q
MODULATOR
Q INPUT
I INPUT
5V
5V
2.74k
1%
0°
2.74k
1%
RF
*ZETEX
2.74k
1%
2.74k
1%
2604 F04
(516) 543-7100
Figure 4. Using DAC A and DAC B for Nearly Continuous Attenuation Control and DAC C and
DAC D to Trim for Minimum LO Feedthrough in a Mixer
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC1458/LTC1458L
Quad 12-Bit Rail-to-Rail Output DACs with Added Functionality
LTC1458: VCC = 4.5V to 5.5V, VOUT = 0V to 4.096V
LTC1458L: VCC = 2.7V to 5.5V, VOUT = 0V to 2.5V
LTC1654
Dual 14-Bit Rail-to-Rail VOUT DAC
Programmable Speed/Power
LTC1655/LTC1655L
Single 16-Bit VOUT DAC with Serial Interface in SO-8
VCC = 5V(3V), Low Power, Deglitched
LTC1657/LTC1657L
Parallel 5V/3V 16-Bit VOUT DAC
Low Power, Deglitched, Rail-to-Rail VOUT
LTC1660/LTC1665
Octal 8-Bit/10-Bit VOUT DAC in 16-Pin Narrow SSOP
VCC = 2.7V to 5.5V, Micropower, Rail-to-Rail Output
LTC1821
Parallel 16-Bit Voltage Output DAC
Precision 16-Bit Settling in 2μs for 10V Step
LTC2600/LTC2610/LTC2620
Octal 16-Bit/14-Bit/12-Bit Rail-to-Rail DACs in 16-Lead SSOP
250μA per DAC, 2.5V to 5.5V Supply Range
LTC2602/LTC2612/LTC2622
Dual 16-Bit/14-Bit/12-Bit Rail-to-Rail DACs in 8-Lead MSOP
300μA per DAC, 2.5V to 5.5V Supply Range
2604fd
16 Linear Technology Corporation
LT 0309 REV D • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2004
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